The present device relates to a counter track joint. The joint may include an outer joint part, an inner joint part, a plurality of torque transmitting balls and a cage. Different designs of track pairs may be formed with the outer joint part and inner joint part, which form opening angles on opposite sides of the constant velocity ball joint.
Counter track joints of this type are disclosed generally in DE 102 20 711 A1, which describes joints with six balls or eight balls. Here the type of ball tracks corresponds to a type known as a Rzeppa joint (RF joints) and from the undercut-free joints (UF joints). This means that the centerlines of the ball tracks consist of uniform radii (RF joint) or that they are composed of radii and parallax lines (UF joint).
In the counter track joints described in DE 102 20 711 A1, the axial opening directions of the track pairs may vary along the circumference. However, the articulation angle of these counter track joints is generally limited to approximately 45°. Articulation angles in excess of 45° may allow a first ball to escape from the first track pairs in the joint articulation plane.
DE 103 37 612 A1 also describes ball track joints in which the track centerlines of the first track pairs (which have an opening angle whose direction of opening points towards the bottom of the joint when the joint is extended) are designed so that the opening angle has its direction of opening reversed from a certain articulation angle when the joint is bent. This is realized in particular in that the track centerlines of the ball tracks of the first track pairs are S-shaped, and therefore include an inflection point.
DE 100 60 220 A1 describes counter track joints in which the centerlines of the first outer ball tracks close to the joint opening have an inflection point so that the centerlines of the first outer ball tracks are S-shaped. In terms of symmetry, the same is true for the centerlines of the first inner ball track of the inner joint part. The maximum articulation angle of these counter track joints may therefore be further increased.
Reference is also made to a counter track joint with a track inflection point, as described in WO 2006/048032. The counter track joint configuration described therein may reduce the friction between the ball cage and the outer joint part or inner joint part. For this purpose it is proposed that the track centerlines of the first track pairs each have an inflection point and that the center angle at the inflection points, related to the central joint plane, be greater than 4 degrees. This helps ensure that the joint operates as a counter track joint in service life operation. Service life operation is considered to be operation within the service life angle at which the service life of the joint is reached without damage under variable load.
In particular applications, however, such constant velocity ball joints are subject to high loads. For example, it may happen that they are installed so that a certain articulation angle is achieved with the constant velocity ball joint even when the motor vehicle is not turning, due to a larger than usual suspension travel. For these particular applications it is important, on the one hand, to provide large articulation angles, but on the other, to provide a suitable service life even where the articulation angle varies within a wide range.
The present device provides a constant velocity ball joint that can be operated reliably and continuously with a large articulation angle. The constant velocity ball joint provides a small design, low heat development during operation, and quiet running.
The constant velocity ball joint may include an outer joint part that has a connection side, an opening side and a cavity bounded by an inner surface, as well as first outer ball tracks and second outer ball tracks extending on the inner surface between the connection side and the opening side. The constant velocity joint may also include an inner joint part that is positioned in the cavity of the outer joint part and has connection means for a shaft running in the direction of the opening side of the outer joint part, and first inner ball tracks and second inner ball tracks extending on an outer surface. A first outer ball track and a first inner ball track each form a first track pair, and a second outer ball track and a second inner ball track each form a second-track pair. When the constant velocity ball joint is not articulated, the first track pairs form a first opening angle in a central joint plane relative to the connection side of the outer joint part, and the second track pairs form a second opening angle in the central joint plane relative to the opening side of the outer joint part. A ball may be disposed in each track pair. A cage, which is also arranged in the cavity between the outer joint part and the inner joint part, has a plurality of cage windows, each of which may receive at least one ball. The first track pairs each form a first track centerline that has a first inflection point, and the second track pairs each form a second track centerline that has a path other than a circular path in a section between the central joint plane and the connection side.
The constant velocity ball joint is, in particular, a joint in the manner of a so-called counter track joint. Here full use can be made, in particular, of the introductory statements regarding the prior art and the explanations contained therein for defining the counter track joint.
Regarding the outer joint part, it should be noted that this is generally of a bell-shaped design, the side from which the cavity can be reached representing the opening side. The axially opposing side is generally referred to as the connection side.
While the cavity has a shape that generally corresponds to that of a bell, an even number of outer ball tracks are generally arranged on its inner surface, for example six, eight, ten or even twelve. These ball tracks are inserted in the manner of recesses in the outer joint part, starting from the cavity. Consideration must now be given to the fact that these ball tracks have two different designs, which is why they are called first and second outer ball tracks. The first ball tracks and the second ball tracks may be alternately arranged in the circumferential direction of the outer joint part.
The inner joint part may be generally designed in the manner of a hub and is provided in the central region with an opening into which a shaft, for example, can be inserted for transmitting a torque. The opening may also be configured to include a keyway connection, or the like, to the shaft. Moreover, the inner joint part has a relatively complexly shaped outer surface into which ball tracks running substantially in an axial direction also extend. The number of inner ball tracks corresponds to the number of outer ball tracks, wherein the relative association of the first and second ball tracks is also predetermined.
With the inner joint part arranged in the cavity of the outer joint part when the constant velocity ball joint is not articulated (articulation angle=0°), it can be seen, in different sectional planes through the longitudinal axis of the outer joint part on the one hand, and the ball tracks on the other, that a first outer ball track and a first inner ball track each form a track pair, as do a second outer ball track and a second inner ball track. A constant velocity ball joint arranged in a non-articulated position may also be described as being axially extended or having aligned axes of the outer joint part and the shaft.
Tangents to the points of the ball tracks that lie within a central joint plane arranged perpendicular to a longitudinal axis of the outer joint part, which runs through the joint center, form an opening angle. The opening angle refers, in particular, to the direction in which the angle opens. The first track pairs form an opening angle to the connection side, and the second track pairs form an opening angle to the opening side.
The track pairs each receive balls transmitting a torque. The term “ball” is used as a generic term for all suitable torque transmitting bodies. The cage, which is positioned between the outer and inner joint parts, serves at least temporarily, during the operation of the joint, to guide the balls in the track pairs. The cage normally has as many cage windows as it receives balls, but it is also possible for a plurality of balls, for example two, to be arranged in a cage window.
To achieve an extremely large articulation angle, the first track pairs may include a first inflection point relative to their track centerline. In particular, the track centerline may have an S-shape. This allows material of the outer joint part close to the opening side to be removed while allowing the balls to remain in contact with the inner region of the outer joint part across a larger articulation angle.
At a particularly large articulation angle, in which the balls in the first track pairs are displaced substantially outwards, there is a corresponding very large inward displacement of the balls into the second track pairs. In this case, increased noise development, or even a risk of component failure, has been observed in prior constant velocity ball joints in the durability range under high load. To help prevent this from occurring, the second track pairs each form a second track centerline that has a path other than a singular circular path in a section between the central joint plane and the connection side. This allows the second track centerline to be adapted in this region to correspond to the shape of the first track pairs close to the opening side. Among other things, this also means, if necessary, that as the outer joint part expands close to the opening side, a correspondingly increasing deepening of the outer, in particular opposing, other ball tracks takes place in the region of the connection side. It is possible in this way to alter the path of the track centerlines, which normally follows a singular circular path close to the connection side of the outer joint part in previous constant velocity ball joints. Here it is possible that at least one further radius of curvature and/or one further straight line section form part of the track centerlines in this section. This allows the reduction in the depth of the outer ball track to be reduced in the direction of the connection side, stopped, or is at least partially changed to an increase in depth.
The second track centerline may have at least a first arc section with a first radius of curvature and a second arc section with a second radius of curvature. Consequently, the variant is described here which is designed without a straight section and, in particular, with only exactly two different arc sections. In this case the first arc section may extend beyond the central joint plane, wherein the second curvature radius section connects tangentially.
In one variant, the second radius of curvature of the second arc section is greater than the first radius of curvature. The radii of curvature have the same orientation and the curvature sections are each seen as concave from one side of the second track centerline.
However, it is also possible for the second arc section to have a second radius of curvature that has an orientation different from the first radius of curvature. The second track centerline in this section therefore has a concave and a convex partial section. In this particular case the second radius of curvature may be smaller than the first radius of curvature.
According to a one configuration of the constant velocity ball joint the second track centerline may have in this section at least a first arc section with a first radius of curvature and a straight line section. Under certain circumstances it may be easier to manufacture such a straight line section in terms of series production of such constant velocity ball joints while at the same time taking advantage of a larger contact angle of the balls and/or greater track depth. The straight line section connects tangentially to the first arc section.
A first small distance point of the first track centerline and a joint center forms a first smallest distance and a second small distance point of the second track centerline and the joint center forms a second smallest distance, wherein the following ratio is maintained:0.95<second smallest distance/first smallest distance<1.0.
If this ratio is maintained, an adequate contact angle of the outer joint part around the balls may be achieved in the second outer ball track, even at the maximum articulation angle. The small distance points of each track centerlines are located at a point where a circle around the joint center with the smallest radius forms a single tangent point (i.e., the small distance points) with the respective track centerline. A corresponding ratio is given with regard to the respective base lines of the outer ball tracks.
The second track centerline in the section may have at least two partial sections with a constant path, wherein the first partial section connecting to the central joint plane is smaller than the second partial section close to the connection side of the outer joint part. This indicates the articulation angle at which a modification of the second track centerline will take place.
The second partial section begins close to the connection side in the region of the balls when the opposing balls are positioned at the inflection point of the first outer ball track. The second partial section may be at least twice as large as the first partial section.
The constant velocity ball joint described herein may be used in a motor vehicle, for example, or any other device employing a constant velocity ball joint.
Since the track centerlines are determined essentially by the contour of the outer joint part and inner joint part, the various features of the device can therefore also be demonstrated on the component parts and the parts correspondingly characterized.
Another aspect of the constant velocity ball joint relates to an outer joint part that has a connection side, an opening side and a cavity bounded by an inner surface. The constant velocity ball joint may also have first outer ball tracks and second outer ball tracks extending on the inner surface between the connection side and the opening side. A first outer tangent on the first outer ball tracks forms a third opening angle in a central joint plane with a first longitudinal axis of the outer joint part relative to the connection side, and a second outer tangent on the second outer ball tracks forms a fourth opening angle in a central joint plane with the first longitudinal axis of the outer joint part relative to the opening side. The second outer ball tracks each form a second outer contour line which has a path other than a circular path in a section between the central joint plane and the connection side.
While account is taken, with regard to the constant velocity ball joint, of the opposing ball tracks of a track pair in the sectional plane of the joint center, only the tangent in the outer ball trajectory and the longitudinal axis of the outer joint part are considered here. In this case the third opening angle does not normally coincide with the first angle, but represents an independent feature of the outer joint part. For an explanation it is also pointed out that a contour line refers, in particular, to the track baseline or a line running parallel with it, for example that of the ball center if this passes the track baseline.
The constant velocity ball joint may have an inner joint part that includes connection means for a shaft running in the direction of the opening side of the outer joint part, as well as first inner ball tracks and second inner ball tracks extending on an outer surface. A first inner tangent on the first inner ball tracks forms a fifth opening angle in a central joint plane with a second longitudinal axis of the inner joint part relative to the connection side, and a second inner tangent on the second inner ball tracks forms a sixth opening angle in a central joint plane with the second longitudinal axis relative to the opening side. The second inner ball tracks each form a second inner contour line that has a path other than a circular path in a section between the central joint plane and the opening side.
The path of the contour line relative to the inner joint part is essentially mirror symmetrical to that of the outer joint part, since the opposite sides of the outer and inner joint parts are in contact with the ball when the constant velocity ball joint is deflected. The contour lines of the outer and inner joint parts may not, however, overlap in full mirror symmetry due to minor deviations that may be required to achieve sufficient tolerance or clearance for the balls inside the track pair during the operation of such a constant velocity ball joint.